Light-sensitive baryta-coated photographic paper



FIG. 2.

g, FORMALDEHYDE R40- 8 Q A GA YOXAL o 5 1 0 1. 5 F1 HAKDENER ,6? 1.5%FORMALDEHYDE I40 '8 Q /20 7.5% h GLYOXAL/ 80 g 60 4 GEORGE R. CLARKLLOYD F. MILLER Z0 INVENTORS 0.3 1 FORMALDEHYDE Jamil) 9.)! u l l I 0 48 I2 I6 20 24 (41% 9.9M

June 16,- 1953 G. R. CLARK ET AL 2,642,362

LIGHT-SENSITIVE BARYTA-COATED PHOTOGRAPHIC PAPER Filed March 18, 19495/1. VER HAL/DE EMULSION G L YOXAL HA RDENED GELA 77N0'7 BIRYTA LA YER\PA PER SUPPORT HOLD/N6 TIME (HRS) ATTORNEY w AGENT Patented June 16,1953 LIGHT- SENSITIVE BARYTAe COATED PHOTO GRAPHICPAPER George R. Clarkand Lloyd F; Miller, Rochester, N. Y., assignors to. Eastman KodakCompany, Rochester, N. Y., a corporation of New Jersey Application March18, 1949; Serial No; 82,118

1 Claim.

1 This invention relates to the preparation. of light-sensitivephotographic elements and: more particularly to photographic elements;having.

baryta-coated paper supports.

It is a well-known procedure in the art of making photographic paperstoprovide a gelatinobaryta-coated paper support, upon which is coated .alight-sensitive silver halide emulsion layer- The over-all physical and.chemical characteristics of the sensitive paper are reflections of thequality of the sensitive emulsion layer; the gelatino-baryta coating:and the paper stock carrying: these layers; For example, physicalirregularities: present on the. surface. of a baryta' coated'paper. are.reflected andpftimesmagnified in subsequentv sensitizing and, processingoperations partly because these. defects prevent the application of auniform emulsion layer during mosphere of the coating alleyswhich is adefinite hazard.

One' object of our invention therefore is to provide baryta-coatedphotographic papers havmg improved. photographic qualities. Anotherobgectris to provide a method of stabilizing the coating characteristicsof baryta coating comthe sensitizing operation. It is thereforeessential, during the baryta coating operation, to apply the. barytacomposition in a uniform and consistent manner so that. maximum. qualityof product can be assured.

Physical non-uniformities in baryta coatings.

in part can be attributed to variations inthe physical and handlingproperties of the: liquid coating compositions and more basically"appear to be markedly influenced by the manner in which the gelatin ofthe baryta coating is hardened. That is, a given gelatino-barytacomposition containing formaldehyde or chromium chloride hardeningagents when freshly made from a predetermined formula can be expected tocoat without difiiculty; however, if, because of circumstances beyondcontrol of the operator, the composition must be held for coating at alater time, it is not uncommon to find the composition useless becausethe viscosity and flow characteristics have changed to the extent thatthe machine will not coat a uniform layer on the paper stock. Thisdifliculty has been attributed to the chemical action of formaldehyde orchromium chloride on the gelatin in the composition.

Similarly, baryta coatings hardened by means of formaldehyde andchromium chloride or similar gelatin hardening agents do not possess theoptimum degree of hardness. As a result, during processing of exposedphotographic papers,

the processing solutions may unduly soften the baryta coating and causereticulation of the emulsion layer. Other disadvantages of the usua1hardeners for baryta layers, particularly formaldehyde, lie in the factthat during the drying of such coatings large quantities of theirritating formaldehyde fumes are released to the atpositions. Otherobjects of our invention will become apparent from consideration ofthe'following'description of our invention. I

The objects of our invention are accomplished principally by utilizingglyoxal as a gelatin hardeningagent in gelatino barytacoatingcompositions.

We have discovered that when glyoxal is used as a gelatin hardeningagent in baryta coat,- ings most of. the; objections to other hardeningagents are overcome. In addition, the novel hardening agent ismoreeflicient since appreciably less of the new hardening. agentneed be usedto obtain. as good. or better hardeningthan is obtainable with otherhardening agents.

In the accompanyingdrawingst in Fig. l.v is shown in greatly enlarged.cross+sectional view,

the. appearance of a photographic; element of.

our invention. and in. Figs. 2 and 3, by meansof. graphicalrepresentation are. compared theaviscosity stabilizing qualities ofglyoxal and formaldehyde.

Our invention will be understood by consideration of the followingexample which is merely illustrative of our invention:

Example A suitable quantity of gelatin is swelled in tepid water anddispersed by melting in approximately five times the weight of water.Blane fixe paste comprising approximately 55 per g cent barium sulfateis then added to the gelatin solution in the quantity required to obtainfrom 20 to 5 0 per cent baryta in the final coating composit1on. Thecomposition is then diluted with water to give the requiredconcentration of solids, following which an aqueous solution of glyoxalis added. Following addition of the customary defoaming or wettingagent, the pigment composition is then passed through dispersionequipment such as a colloid mill to increase the degree of dispersion ofthe baryta particles in the gelatin solution, and the dispersion isready for coating on a paper support. Coatings on paper are made in theconventional manner and at this point the superior coating properties ofthe composition become most evident. It is observed that thecompositions uniformly wet the paper stock with the result that a barytalayer of uniform thickness and freedom from irregularities results whenthe coating is subsequently dried down in the coating alley. Preferably,following calendaring of the baryta-coated sheet, a light-sensitivesilver halide emulsion layer is applied in a manner well known in theart. The product would appear substantially as shown in Fig. 1 of theaccompanying drawings wherein the paper support I0 is shown as carryingthe glyoxal-hardened gelatino-baryta layer and the silver halideemulsion layer 12 over the baryta layer.

In the above example, the concentration of gelatin in the coatingcomposition may be varied from about 1 to 15 per cent by weight and theglyoxal (added as an aqueous solution of strength of from about 1 to 40per cent) is added to obtain a concentration of from about 1 to 6 percent based on the weight of gelatin present. In general, 2 per centglyoxal produces satisfactory hardening.

We have mentioned that glyoxal is more efficient as a hardening agent inbaryta compositions than other hardening agents and particularly incomparison with formaldehyde we find that glyoxal is at least six timesas eiiicient and this is rather unexpected considering that the compoundcontains in its molecule only twice as many reactive aldehyde groups asdoes formaldehyde.

This increase in efficiency becomes quite evident when baryta coatingsare cured down under conditions of high temperature and humidity whichtend to volatilize formaldehyde rapidly. Under such conditions glyoxaltends to be retained by the product during the hardening period.

Fig. 2 of the accompanying drawings illustrates the advantage from aviscosity standpoint of using glyoxal as a hardener. The graph showsthat as the concentration of glyoxal (based on the weight of gelatinpresent) in a formula compounded as in the above example, is varied from1 to 15 per cent, the viscosity remains reasonably constant; Whereasover the range of from 5 to 15 per cent, the compositions containingformaldehyde steadily increase in viscosity. Therefore, since machineoperating conditions must be varied with changes in viscosity of thecoating compositions, when using formaldehyde the manufacturer must coatunder a Wide variety of machine operating conditions to obtain qualitycomparable to glyoxal-hardened coatings.

Fig. 3 of the drawings illustrates the viscosity eiiect of holdingtypical baryta formulas containing formaldehyde and glyoxal as hardeningagents. According to the graph, at concentrations of 0.3 per centhardener, the increase in viscosity over the 24-hour holding periodincreses more using formaldehyde; whereas at concentrations of 1.5 percent, which is the more common hardener concentration, the viscosity ofthe formaldehyde compositions reaches excessive values in considerablyless than 4 hours of holding time; while the viscosity of the glyoxalcompositions has not increased to the extent that the solutions are notusable. This advantageous behavior of glyoxal as a hardener agentappears quite unexpected when considering the fact that the compound hastwo reactive aldehyde groups in its molecule compared to formaldehydeand on this basis might be expected to produce greater viscosityincreases than does formaldehyde.

It is to be understood that the disclosure herein is by way of exampleand that We consider as included in our invention all modifications andequivalents falling within the scope of the appended claim.

What we claim is:

A light-sensitive photographic element comprising a paper support havingon one surface thereof a gelatino-baryta layer containing glyoxaluniformly dispersed therein as a gelatin hardening agent, and over saidlayer a silver halide emulsion layer.

GEORGE R. CLARK. LLOYD F. MILLER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,870,354 Brunken Aug. 9, 1932 2,309,492 Albers et al Jan. 26,1943 2,414,858 Davidson Jan. 28, 1947

